docs: def begin(self, service_endpoint):
          """Create an AuthRequest object for the specified
          service_endpoint. This method will create an association if
          necessary."""
          if self.store is None:
              assoc = None
          else:
              assoc = self._getAssociation(service_endpoint)
  
          request = AuthRequest(service_endpoint, assoc)
          request.return_to_args[self.openid1_nonce_query_arg_name] = mkNonce()
  
          if request.message.isOpenID1():
              request.return_to_args[self.openid1_return_to_identifier_name] = \
                  request.endpoint.claimed_id
  
          return request